1. Field of the Invention
The present invention relates to an ultrasonic inspection and imaging instrument and, more particularly, relates to an ultrasonic inspection and imaging instrument using burst waves which permits ultrasonic measurement and imaging at high resolution with a simple operation without using high frequency signals, which have been necessary for high-resolution ultrasonic measurement and imaging.
2. Description of Related Art
An ultrasonic inspection and imaging instrument is capable of displaying the interior of an object to be inspected (a sample) in the form of a B- and a C-scope image. In order to obtain a clear image, an imaging instrument of this sort requires inputting of various measurement conditions including specifications of an ultrasonic probe (hereinafter Probe) such as the focal distance, the wave velocities at the current temperatures in the interior of a medium and the sample and the like, and in response thereto setting of the focus of the probe in the sample at a desired depth, a gate position, a gate width and the like.
When inspecting ICs with an ultrasonic inspection and imaging instrument, it is required to obtain an image with a high resolution at an interface in a thin sample such as a junction face between a semiconductor chip and a lead frame. For this reason it is required to use a probe having a high oscillation frequency and a narrow frequency band as well as to use an ultrasonic flaw detector having an excellent amplification characteristic at a high frequency. In addition thereto, it is further required to properly focus the probe and to set the gate position and the gate width which is still further required to be set as narrow as possible.
An ultrasonic inspection and imaging instrument of high resolution generally becomes expensive and requires skill for the measurement operation as the resolution thereof increases. Unlike the above, there are ultrasonic inspection and imaging instruments which permit to increase the resolution without using a high frequency. One of such ultrasonic inspection and imaging instruments makes use of an interference wave caused by an echo S from the surface of a sample and an interface echo F from an interface in the same, and another makes use of an interference wave caused by a lens echo and a sample echo. In these ultrasonic inspection and imaging instruments the ultrasonic wave used for the measurement is a burst wave (continuous wave) other than a pulse wave.
The ultrasonic inspection and imaging instruments making use of the burst wave are comparatively inexpensive because of the non-use of the high frequency- However, when observing a reflection wave (an A scope image) from a sample by making use of an oscilloscope and the like, an echo from the surface of the sample and an echo from the interface in the sample are observed as if a series of a continuous wave as shown in FIG. 6(b) which will be explained later therefore the focusing of the probe and the setting of the gate position are very difficult such that nonexperienced persons cannot handle instruments of this type.
Unlike the case of using pulse waves in which an operator discerns and determines the interface echo from the sample, the operator has to set a gate for sampling out a proper measurement image by selecting, through repeated trial and error, a gate position for obtaining an image having the most desirable resolution (a resolution representing a well-formed image in view of the image itself is called imaging resolution) while gradually shifting the gate position for a series of burst waves.
The above is also true with regard to the gate width. In a burst wave measurement wherein a gate having a broad width to the extent covering all interference waves is set, the gate width is normally insignificant. However, in order to increase the imaging resolution, in other words, in order to eliminate influences from portions other than noted portions, it is necessary to note a specific portion among the entirety of the interference waves and to extract the portion through the gate. In such case, it is necessary to set a gate having a comparatively narrow width at a proper position. In order to determine a proper gate width in such instance it is necessary to perform setting operations many times with various gate widths.
Further, with regard to the distance between the probe and the sample, a position which shows the most desirable resolution also has to be determined through trial and error while gradually varying the distance. In addition, it is further required to adjust the frequency of the burst wave in order to obtain a proper image.
In order to avoid the repetition of these operations as much as possible, with an ultrasonic inspection instrument using a pulse wave generator suitable for obtaining an image of a low resolution, an image at the interface in a sample is obtained beforehand and the gate position, gate width and distance between the probe and the sample at this instance are recorded. Thereafter the previously recorded gate position, gate width and distance between the probe and the sample are set for another ultrasonic inspection instrument using a burst wave generator.
However, with the above measurement it is necessary to use two sets of measurement instruments, and the gate position, gate width and distance between the probe and the sample which are obtained through the measurement instrument using a pulse wave generator suitable for obtaining an image of a low resolution are not necessarily proper ones for the measurement instrument using a burst wave generator. The probes themselves are different; in particular, the frequencies of the pulse wave and the burst wave used for the respective probes are different. Further, their signal transmission passages during signal transmission and reception are different. Still further, their beam routes according to the focusing positions are different.
These causes, in particular, affect the gate position. A relatively proper gate width can be determined when successively selecting gates from one having a broad width to one having a narrow width. Further, a relatively proper position for the probe is also determined when successively moving the probe toward an object or alternatively moving the probe away from the object. However, the above operations are based on a condition that the gate position is properly set. The gate position varies depending upon such as an object to be inspected and a flaw position, and has to be determined every time the object to be inspected is changed.
As a result, even when the two sets of measurement instruments are used, it takes time for adjusting operations for the measurement instrument using a burst wave generator and the measurement operations therewith are complex.